Recent advances in the research concerning chemical mediators of inflammatory and allergic reactions have implicated two profoundly active lipids, viz. platelet activating factor and members of the leukotriene family. These lipids have strikingly similar, pharmacological actions and evidence suggests a close biochemical interaction between these substances. While there are assays for the LTs based on biological activity, RIA, UV and HPLC properties, there exists only biological assays for PAF. Detailed studies of AGEPC (acetyl glycerol ether phosphocholine) which has been described as the structure of PAF, have been hampered without a specific, sensitive method of analysis. This need is important to more fully evaluate the physiological role for AGEPC in health and disease. We propose to develop physico-chemical methods of quantitative analysis of AGEPC and its lyso-analog based on fast atom bombardment mass spectrometry and GC-MS using stable isotope techniques. These techniques will be used to determine accurate concentrations of AGEPC in physiological fluids. In addition we propose to examine the possible biochemical interaction between the stimulation of AGEPC synthesis and leukotriene synthesis in polymorphonuclear leukocytes, macrophages, and pulmonary endothelial cells using FAB-mass spectrometry. Metabolites of AGEPC in these cells will be studied. Finally FAB-MS methods will be developed to study the incorporation of exogenous deuterium-labeled arachidonic acid into various classes and specific species of phospholipids in PMNs which can be stimulated by AGEPC. These studies are directed towards understanding the basic biochemical events involved in mediator biosynthesis. It is by understanding the specific biochemical events surrounding PAF and LTs that the development of specific pharmacological agents antagonistic to these mediators may be possible.